Wireless industrial networks represent a key enabler for Industry 4.0. Since wireless links are known to be lossy, most deployments rely on scheduled transmissions to avoid collisions. Software Defined Networking (SDN) is a famous architecture where a controller centralizes all the configuration. In a scheduled wireless network, the SDN paradigm has to be extended to allocate both paths and bandwidth. Unfortunately, most solutions address only the initial configuration, which becomes suboptimal when the link quality evolves, or the conditions change. We propose here the mechanisms for continuous optimization. We define how control packets can reconfigure the data plane while guaranteeing a globally consistent state, even when the control plane exploits unreliable links. No data packet is dropped because of inconsistent forwarding rules. To be energy efficient, we also propose a scheduling algorithm that minimizes the network reconfiguration to minimize the overhead. Our simulation results highlight the strength of our proposition to handle topology and link quality changes.

The Industrial Internet of Things (IIoT) has now emerged for many industrial applications. However, many critical applications require high reliability and bounded end-to-end latency. Fortunately, scheduled wireless networks such as IEEE 802.15.4-TSCH try to orchestrate finely the transmissions. In particular, the Software-Defined Networking (SDN) paradigm is promising to concentrate the intelligence of the network in a controller and to simplify the functions achieved by the motes. SDN controller relies on link quality information of wireless devices to construct the routing topology of the network and to provision adequate radio resources for each link. We propose here an accurate link quality estimation scheme based on the SDN-TSCH, as an SDN solution for IEEE 802.15.4-TSCH network. We exploit the centralized view of the SDN controller to transmit packets of link quality estimation in a collision-free manner. Moreover, we investigate the performance of the control plane of SDN-TSCH through different shared, dedicated, and hybrid (mix of shared and dedicated cells) approaches. We figured out that the dedicated control plane provides high reliability and fast convergence for wireless SDN networks.

Industrial wireless sensor networks (IWSNs) play a key role in the Industry 4.0 revolution. The network infrastructure is critical to interconnect sensors and actuators and needs to respect key performance indicators. IEEE 802.15.4-TSCH is a candidate technology for IWSN since it relies on scheduled transmissions and frequency hopping to make the network more reliable. However, distributed scheduling solutions fail to provide high-reliability and low-end-to-end latency. Software defined network (SDN) tends now to emerge in wireless networks as well, where a controller is in charge of the whole network configuration. But scheduled wireless networks require to go beyond usual SDN forwarding rules by including the radio resource allocation (dedicated time-frequency blocks). Moreover, radio links are known to be unreliable, and we need to adapt the control and data planes to make the network efficient. We propose SDN-TSCH to orchestrate a scheduled network adapting the SDN paradigm. More specifically, the controller is in charge of 1) selecting the time source; 2) maintaining a tree structure for the control plane, with scheduled resources dedicated to the control plane; and 3) installing a new data flow while guaranteeing flow isolation. We also propose a very efficient link quality estimation technique tailored for scheduled TSCH networks. Our simulations highlight that the SDN controller can allocate in SDN-TSCH just-enough resources to respect both latency and reliability constraints.

The Industrial Internet of Things (IIoT) applications need to rely on a wireless infrastructure able to provide low end-to-end latency, and high reliability. Software-Defined Networking (SDN) is promising to make the network more agile, pushing the decision process to a controller. However, radio links are unstable while the controller needs to construct an accurate view of the network to schedule the transmissions efficiently. We propose here SDN-TSCH to separate the data and control planes for a scheduled network. We construct a reliable control plane, maintaining a collision-free path to and from the controller. Besides, SDN-TSCH guarantees flow isolation: each flow can reserve dedicated resources so that end-to-end reliability and latency constraints can be respected per flow. Finally, we also dedicate resources for best-effort traffic, to accommodate various applications. Our Cooja simulations highlight the flow isolation characteristics of SDN-TSCH: we provide very high reliability even in presence of best-effort traffic.

Time-Slotted Channel Hopping (TSCH), as an operational mode of the IEEE 802.15.4 standard, is a promising medium access mechanism for industrial Wireless Sensor Networks (WSNs). However, efficient performance of such networks depends on the medium access scheduling scheme, which is not specified by the standard. This paper proposes a low-latency distributed scheduler, called LaDiS, for multi-hop tree-based TSCH networks. The main objective is to provide low end-to-end data latency in convergecast WSNs with very low communication overhead. The schedule of each node is determined by its parent based on the available local information about the routing structure and traffic requirement of that node. At the same time, LaDiS provides proper opportunity for data aggregation by relaying nodes in a multi-hop network leading to reduced traffic. The performance of the proposed scheduler as well as the existing distributed TSCH schedulers is extensively evaluated in various setups. The results show that LaDiS considerably outperforms others in terms of data latency in the networks under consideration in this work. LaDiS is implemented and integrated in the Contiki operating system.

Wireless Body Area Networks (WBANs) have made their way into many smart and ubiquitous healthcare and wellness applications. A low-power, efficient, and reliable communication protocol is of paramount importance for the success of WBANs in satisfying the requirements of the health applications. The IEEE 802.15.4 standard is always one of the main options due to its efficiency and low-complexity. However, it suffers from the impact of other wireless technologies using the same frequency band such as WiFi and Bluetooth. Time Slotted Channel Hoping (TSCH) is an operational mode of the IEEE 802.15.4e standard, which is originally developed for reliable industrial wireless networks. TSCH has Time Division Multiple Access (TDMA) and frequency hopping features, which increase the network robustness against effects such as noise, interference, and multi-path fading. This paper proposes to exploit TSCH for communications in WBANs, and studies its performance. The features of TSCH like power efficiency, TDMA-based operation, and heterogeneity support fit very well with the requirements of many health monitoring applications. The performance of the TSCH standard for WBAN communications is investigated through real-world experiments in various conditions. The results show that TSCH outperforms the basic IEEE 802.15.4 standard in terms of communication reliability against interferences from coexisting wireless devices.